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Publication numberUS5526324 A
Publication typeGrant
Application numberUS 08/515,580
Publication dateJun 11, 1996
Filing dateAug 16, 1995
Priority dateAug 16, 1995
Fee statusLapsed
Also published asWO1997007496A1
Publication number08515580, 515580, US 5526324 A, US 5526324A, US-A-5526324, US5526324 A, US5526324A
InventorsWilliam B. Cushman
Original AssigneePoiesis Research, Inc.
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Acoustic absorption and damping material with piezoelectric energy dissipation
US 5526324 A
Abstract
Acoustic absorption and vibration damping materials are produced by mixing electrically conductive particles or strands into a piezoelectric matrix material. The electrically conductive particles or strands act as small localized electrical short-circuits within the matrix material and effectively dissipate the electric charges produced by piezoelectric effect from the pressure of acoustic or vibrational energy as heat. All energy thus converted into heat is subtracted from the original acoustic or vibrational energy, resulting in acoustic absorption and/or vibration damping.
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Claims(9)
I claim:
1. An acoustic absorption or vibration damping material comprised of a piezoelectrically active matrix material with a plurality of electrically conductive particles incorporated and embedded therein such that said electrically conductive particles are substantially encapsulated and enclosed within and by said piezoelectrically active matrix material.
2. The acoustic absorption or vibration damping material of claim 1 where said matrix material is polyvinylidene fluoride.
3. The acoustic absorption or vibration damping material of claim 1 where said electrically conductive particles are made from graphite.
4. The acoustic absorption or vibration damping material of claim 1 where said electrically conductive particles are made from a metal.
5. An acoustic absorption or vibration damping material comprised of a piezoelectrically active matrix material with a plurality of electrically conductive strands incorporated and embedded therein such that said electrically conductive strands are substantially encapsulated and enclosed within and by said piezoelectrically active matrix material.
6. The acoustic absorption or vibration damping material of claim 5 where said matrix material is polyvinylidene fluoride.
7. The acoustic absorption or vibration damping material of claim 5 where said electrically conductive strands are made from graphite.
8. The acoustic absorption or vibration damping material of claim 5 where said electrically conductive strands are made from a metal.
9. The acoustic absorption or vibration damping material of claim 5 where said electrically conductive strands are long fibers.
Description
BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to acoustic absorption and damping materials, and more particularly, to acoustic absorption and damping materials that utilize a piezoelectric phenomenon to convert mechanical energy into electrical energy and to subsequently dissipate the converted energy as heat.

2. Description of Related Art

Absorbing or damping unwanted acoustic or vibrational energy involves converting that energy into another form, usually heat. At the molecular level, the only distinction between heat energy and acoustic or vibrational energy is the randomness of the vector directions of molecular displacements. Acoustic and vibrational energy is highly correlated with large numbers of molecules displacing at the same time and in the same direction. Heat in a particular object may well have the same or more energy than propagating acoustic or vibrational energy, but the motion of the molecules is random with the mean molecular displacement at any given location being near zero.

Two primary techniques are available for randomizing the vector directions of the molecules in a matrix material propagating acoustic or vibrational energy. Cushman, et al. (U.S. Pat. No. 5,400,296) teach the use of two or more species of particles with differing characteristic impedances in a matrix material to promote random internal reflections at boundaries within the matrix material and the subsequent increase in probability that phase cancellation at adjacent or nearby locales can take place. Single particle species may also be used in this manner, but with less effect. Phase cancellation effectively randomizes the vector direction of molecular movement where it occurs. A second approach involves the careful choice of materials that exhibit a high degree of internal hysteresis. This internal hysteresis is thought to be caused by metastable molecular energy levels within the material. Propagating acoustic or vibrational energy may boost a particular molecule into a higher energy level, thus subtracting that energy from propagating energy, where the molecule remains for some time before randomly returning to its original energy level. For a discussion of this effect see Hartmann and Jarzynski, "Ultrasonic hysteresis absorption in polymers," J. Appl. Phys., Vol. 43 , No. 11, November 1972, 4304-4312.

Instead of randomizing molecular displacements to dissipate propagating acoustic or vibrational energy, some of this energy can be removed by converting the mechanical energy of sound or vibration into electrical energy utilizing the piezoelectric effect. A piezoelectric material such as polyvinylidene fluoride (PVDF) may be polarized and a coating of a conductive material such as aluminum applied to produce a piezoelectric transducer that will convert acoustic energy into electric energy, thus facilitating removal of converted energy from the system. This approach is reported in a recent issue of the Japan New Materials Report (May-June, 1995, p 9). In this report acoustic energy reductions of up to 90% are claimed in material specimens only 10 to 30 microns thick. However, the need to polarize the material and apply conductive electrodes to tap off the electrical energy produced limits the usefulness of this technique.

SUMMARY OF THE INVENTION

Accordingly, the object of the instant invention is to provide an improved acoustic absorption and vibration damping material utilizing the piezoelectric effect that may be injection molded, compression molded, or extruded without additional processing.

This and additional objects of the invention are accomplished by mixing electrically conductive particles or strands into a piezoelectric matrix material. The electrically conductive particles or strands act as small localized electrical short-circuits within the matrix material and effectively dissipate the electric charges produced by piezoelectric effect from the pressure of acoustic or vibrational energy as heat. All energy thus converted into heat is subtracted from the original acoustic or vibrational energy, resulting in acoustic absorption and/or vibration damping.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following Description of the Preferred Embodiments and the accompanying drawings, like numerals in different figures represent the same structures or elements. The representation in each of the figures is diagrammatic and no attempt is made to indicate actual scales or precise ratios. Proportional relationships are shown as approximations.

FIG. 1 shows a shows a piezoelectric matrix material of the instant invention with a plurality of embedded electrically conductive particles.

FIG. 2 shows a piezoelectric matrix material of the instant invention with a plurality of embedded electrically conductive strands.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The parts indicated on the drawings by numerals are identified below to aid in the reader's understanding of the present invention.

10. Piezoelectric matrix material.

11. Electrically conductive particle.

12. Electrically conductive strand.

A preferred embodiment of the instant invention is shown in FIG. 1 with electrically conductive particles. In FIG. 1, 10 is the piezoelectric matrix material of the instant invention and may be any piezoelectrically active material. A preferred piezoelectric matrix material is polyvinylidene fluoride (PVDF). The electrically conductive particles, 11, of FIG. 1 are randomly distributed within the piezoelectric matrix material, 10, and act as electrical short-circuits for the piezoelectrically active matrix material. Current flowing in the electrically conductive particles, 11, will cause them to heat due to their resistance. The heat produced in the electrically conductive particles will be dissipated into the piezoelectric matrix material but will have no specific orientation relative to the propagation direction of the acoustic or vibrational energy that produced the electricity that causes heating. That is, the molecular movement of the heat that results indirectly from the piezoelectric effect of the matrix material is random and, additionally, somewhat phase-delayed due to the thermal inertia of the electrically conductive particles. Thus, the correlated molecular movement of propagating acoustic or vibrational energy within the piezoelectric matrix material of the instant invention is decorrelated into heat. A preferred material for the electrically conductive particles is graphite.

A preferred embodiment of the instant invention is shown in FIG. 2 with electrically conductive strands. In FIG. 2, 10 is the piezoelectric matrix material of the instant invention and may be any piezoelectrically active material. A preferred piezoelectric matrix material is polyvinylidene fluoride (PVDF). The electrically conductive strands, 12, of FIG. 2 are randomly distributed within the piezoelectric matrix material, 10, and act as electrical short-circuits for the piezoelectrically active matrix material. Current flowing in the electrically conductive strands, 12, will cause them to heat due to their resistance. The heat produced in the electrically conductive strands will be dissipated into the piezoelectric matrix material but will have no specific orientation relative to the propagation direction of the acoustic or vibrational energy that produced the electricity that causes heating. That is, the molecular movement of the heat that results indirectly from the piezoelectric effect of the matrix material is random and, additionally, somewhat phase-delayed due to the thermal inertia of the electrically conductive particles. Thus, the correlated molecular movement of propagating acoustic or vibrational energy within the piezoelectric matrix material of the instant invention is decorrelated into heat. A preferred material for the electrically conductive strands is graphite.

Many modifications and variations of the present invention are possible in light of the above teachings. For example, any matrix material with piezoelectric activity may be used and any electrically conductive particles, strands, or long fibers, may also be used. It is therefore to be understood that, within the scope of the appended claims, the instant invention may be practiced otherwise than as specifically described.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3515910 *Nov 12, 1968Jun 2, 1970Us NavyAcoustic absorbing material
US3614992 *May 26, 1969Oct 26, 1971Us NavySandwich-type acoustic material in a flexible sheet form
US4628490 *Dec 24, 1985Dec 9, 1986The United States Of America As Represented By The Secretary Of The NavyWideband sonar energy absorber
US5400296 *Jan 25, 1994Mar 21, 1995Poiesis Research, Inc.Acoustic attenuation and vibration damping materials
Non-Patent Citations
Reference
1Hartmann & Javzynski "Ultrasonic hysteresis absorption in polymers" J. Appl. Phys. vol. 43, No. 11, Nov. 1972, 4304-4312.
2 *Hartmann & Javzynski Ultrasonic hysteresis absorption in polymers J. Appl. Phys. vol. 43, No. 11, Nov. 1972, 4304 4312.
3 *Japan New Materials Report, May Jun. 1995, p. 9.
4Japan New Materials Report, May-Jun. 1995, p. 9.
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US5706249 *Apr 1, 1996Jan 6, 1998Cushman; William B.Panel spacer with acoustic and vibration damping
US5745434 *Jan 9, 1997Apr 28, 1998Poiesis Research, Inc.Acoustic absorption or damping material with integral viscous damping
US5754491 *Feb 24, 1997May 19, 1998Poiesis Research, Inc.Multi-technology acoustic energy barrier and absorber
US5911930 *Aug 25, 1997Jun 15, 1999Monsanto CompanySolvent spinning of fibers containing an intrinsically conductive polymer
US6228492Sep 23, 1997May 8, 2001Zipperling Kessler & Co. (Gmbh & Co.)Preparation of fibers containing intrinsically conductive polymers
US6386317 *Dec 21, 1999May 14, 2002Nissan Motor Co., Ltd.Sound-absorbing duct structure
US7837008 *Sep 27, 2005Nov 23, 2010The United States Of America As Represented By The Secretary Of The Air ForcePassive acoustic barrier
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CN102700203A *Jun 15, 2012Oct 3, 2012哈尔滨工业大学Carbon fiber composite material laminated plate with piezoelectric damping and preparation method thereof
CN102700203BJun 15, 2012Oct 29, 2014哈尔滨工业大学一种具有压电阻尼的碳纤维复合材料层合板的制备方法
CN103963398A *Apr 29, 2014Aug 6, 2014中国航空工业集团公司北京航空材料研究院Dual-functional toughening-damping intercalation material and product prepared from same
CN103963398B *Apr 29, 2014May 4, 2016中国航空工业集团公司北京航空材料研究院一种双功能插层材料及制品
CN104527173A *Dec 5, 2014Apr 22, 2015中简科技发展有限公司Composite damping layer toughened thin layer and preparation method thereof
EP0964181A3 *Jun 5, 1999Nov 20, 2002DaimlerChrysler AGMethod and device to influence vibrations resulting from an engine-driven vehicle
EP0964387A3 *Jun 5, 1999Mar 20, 2002DaimlerChrysler AGMethod and apparatus for influencing window-generated noise
Classifications
U.S. Classification367/1, 181/294
International ClassificationG10K11/165
Cooperative ClassificationG10K11/165
European ClassificationG10K11/165
Legal Events
DateCodeEventDescription
Apr 2, 1996ASAssignment
Owner name: POIESIS RESEARCH, INC., FLORIDA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:CUSHMAN, WILLIAM B.;REEL/FRAME:007878/0954
Effective date: 19960328
Jan 4, 2000REMIMaintenance fee reminder mailed
Jun 11, 2000LAPSLapse for failure to pay maintenance fees
Aug 15, 2000FPExpired due to failure to pay maintenance fee
Effective date: 20000611